Unit 7 Flashcards
How do exocrine glands develop?
Exocrine glands develop as invaginations of surface epithelium, induction by connective tissue
How do exocrine glands retain surface connection?
Exocrine glands retain a connection with the surface via ducts.
What is an acinus?
A berry-like cluster of cells with a central lumen that serves as the secretory portion of the secretory vesicles. It produces the secretory product.
What is the conducting portion of a secretory vesicle?
A duct. It may be branched or unbranched. It modifies secretory product by absorption. Ducts may also have secretory functions in some glands.
How are exocrine glands classified?
Simple glands: single unbranched duct. Secretory portion can be branched or unbranched. Examples: sweat glands and sebaceous glands.
Compound glands: multiple branched ducts. Secretory portion can be acing, tubular or tubloacinar. Examples: salivary glands and exocrine pancreas.
What are the 3 different types of secretion?
Holocrine
Apocrine
Merocrine
What is holocrine secretion?
Lysis of cells filled with secretory product. Cells divide and disintegrate, and their contents become the secretion. Example: skin sebaceous gland.
What is apocrine secretion?
Shedding of apical cell segment filled with secretory product. The apical portion pinches off a secretory cell and enters the tubule lumen. Example: mammary glands.
What is merocrine secretion?
Exocytosis of proteins or glycoproteins, Secretory vesicles release their contents by exocytosis. Examples: sweat glands, salivary glands, exocrine pancreas. Called eccrine in sweat glands.
What cell types are found in glandular epithelium in merocrine glands (glands that use exocytosis for secretion)?
Serous cells
Mucus cells
Myoepithelial cells
Serous cells in merocrine glands
Stain well with H & E
Secrete proteins
Abundant RER and Golgi in the basal portion of the cell
Secretory granules in the apical cytoplasm
Mucous cells in merocrine glands
Secrete mucin, made of glycoproteins rich in complex carbohydrates
Mucins stain poorly with H&E – instead stain with periodic acid Schiff (PAS) stain
Abundant RER and Golgi in the basal portion of the cell
Mucin-filled secretory granules in the apical cytoplasm
What happens to mucin upon secretion?
Upon secretion, mucin becomes mucous, a viscous, jelly-like protective lubricant
How are mucuous cells stained?
With periodic acid-Schiff (PAS) stain. They do not stain well with H&E
How are serous cells stained?
H & E
Myoepithelial cells in merocrine glands
Located between the basal lamina and secretory or duct cells.
They have triangular or elongated nucleus
Have long acto-myosin-rich, contractile processes that surround the epithelial cells
Contraction helps expel secretory product from the gland lumen
Present in sweat, salivary, and mammary glands
Where are myoepithelial cells found?
Myoepithelial cells are present in sweat, salivary, and mammary glands
How are ions and fluid transported across the glandular epithelia?
Via ion channels and pumps (ie: Na/K ATPase), using mitochondria as a source of energy. Membrane specializations increase surface area for transport and tight junctions seal off the apical surface from the basolateral surface.. The pumps and transporters are distributed differentially across the surface area.
What are unicellular glands?
Goblet cells in the lining of the small intestine and in the respiratory epithelium of the trachea
What are the similarites and differences between serous and mucous cells in merocrine glands?
Both have: ● RER at the base ● Perinuclear Golgi ● Secretory vesicles in the apical portion ● Exocytosis
Major difference is staining: serous cells with H&E, mucus cells with PAS (periodic acid-Schiff)
What are sebaceous glands?
Multicellular simple, branched, acinar glands. They use holocrine secretion (basal layer of cells proliferate, differentiate into sebocytes,
accumulate lipid droplets, and rupture.
They are associated with hair follicles. The basal layer of cells proliferate and differentiate
What is sebum composed of?
Sebum is composed of triglycerides, cholesterol, squalene, wax esters.
Which glands are responsible for acne?
Sebaceous glands.
● Increased sebaceous gland activity at puberty.
● Hair follicle may become plugged.
● Skin bacteria (Propionibacterium acnes) break sebum into free fatty acids.
● Fatty acids cause irritation and inflammation.
● Inflammation attracts neutrophils, further escalating inflammation.
What are eccrine sweat glands?
Simple, coiled, tubular glands. They use merocrine secretion. They have stratified cuboidal epithelium in the duct and secretory portion.
What stimulations sweat secretion?
Cholinergic fibers of the sympathetic nervous system.
What are the cell types found in the secretory coil?
Pale (clear) cells
Dark cells
Myoepithelial cells
What are pale (clear) cells?
One of the cell types found in the secretory coil. They are pyramidal to columnar in shape. Located at the periphery, resting on the basal lamina. They produce the watery component of sweat and contain abundant mitochondria. They have microvilli and intracellular canaliculli, as well as tight junctions.
What are dark cells?
One of the cell types found in the secretory coil. They are pyramidal in shape and located near the lumen. They secrete glycoproteins and proteins, including bactericidal peptides.
What are myoepithelial cells?
They are located within the basal lamina and have triangular or elongated nuclei. They contain actomyosin-rich processes, which contract to help expel the secretory product.
Describe sweat ducts.
They have a darker staining epithelium than secretory coils. They reabsorb sodium and chloride with abundant Na/K ATPases in the basal membrane. They also have abundant mitochondria and tight junctions.
Describe apocrine sweat glands
● Located in the axillary,
areolar and perineal regions
● Simple cuboidal / columnar
epithelium
● Simple coiled glands
● Merocrine secretion
(despite the name)
● The secretory coil is lined by simple cuboidal epithelium and has large lumen
● Associated with hair shafts
● Stimulated by adrenergic
nerve fibers of the sympathetic nervous system, secretory product may contain pheromones
What is the composition of sweat and how can it be used as a disease indicator?
Water, Ammonia, Sodium, Chloride, Urea, Uric Acid, Organic Compounds, Bactericidal Peptides, Proteolytic Enzymes.
Altered sweat composition may indicate disease:
● Urea frost in uremia (kidney failure)
● Elevated levels of NaCl in sweat in cystic fibrosis
Describe the histological organization of eccrine sweat glands
Stratified cuboidal
epithelium
Secretory portion:
● Pale cells:
Function to secrete fluid
Tight junctions
Membrane infoldings
Abundant mitochondria
Intercellular canaliculi
● Dark cells:
Have RER, golgi and secretory granules
secrete proteins
● Myoepithelial cells:
contractile, actin myosin bundles, contract
to expel product
Conducting portion:
● Re-absorbs
NaCl and water
What is the function and composition of saliva?
To moisten and lubricate the oral cavity, and initiate the digestion of carbohydrates: alpha amylase. Also functions in immune defense: lysozyme, lactoferrin and SIgA. It is also involved in secretion of calcium and phosphate to make acquired pellicle
What happens with reduced function of salivary glands?
Reduced function of salivary glands due to disease or radiotherapy can lead to:
speech difficulties, oral mucosa atrophy, and dental carries.
Note, rabies causes INCREASED function of salivary glands.
Describe the organization of salivary glands
● Connective tissue capsule
● Septa - extensions of the capsule that divide parenchyma into lobules.
● Connective tissue stroma contains:
- Capillary plexus surrounding secretory
and ductal components
- Nerves that control secretion
–parasymp stimulate, symp inhibit
- Lymphocytes and plasma cells
● Parenchyma in the lobules contains salivons: - Secretory acini or tubules - Intercalated ducts - Intralobular ducts
● Interlobular ducts
(in the septa)
What are salivons?
A secretory unit found in the parenchyma/lobules of salivary glands, that contain acini, intercalated ducts, and interlobular excretory ducts.
What is the drainage pattern of acini?
Acini drain into intercalated ducts, intercalated ducts drain into interlobular ducts, intralobular ducts drain into interlobular ducts located in the septa.
Describe salivary gland tumors
● 80% are benign. ● Pleomorphic adenoma: - 65% of benign tumors. - Accumulation of cartilage-like material produced by myoepithelial cells.
Describe the general organization of salivary glands
● Acini or tubules:
- Serous, mucous, or mixed:
- Serous cells: pyramidal in shape, secrete proteins like sIgA. Also secrete bicarbonate and absorb chloride.
- Mucous cells: cuboidal to columnar in shape, secrete mucin (glycoproteins rich in complex carbs)
- Myoepithelial cell (basket cells): reside within the basal lamina, have long, branched contractile processes that prevent secretory portion dissension and accelerate secretion, they’re also present in ducts
- Serous cells: pyramidal in shape, secrete proteins like sIgA. Also secrete bicarbonate and absorb chloride.
● Intercalated ducts:
- Small (4-6 cells in circumference) cuboidal cells that lack secretory granules, they connect the secretory portion to the intralobular duct
● Intralobular ducts:
- More than 6 cells in circumference and lined by simple columnar epithelium. Basal striated in serous glands: basal membrane infolding that house mitochondria. Have active transport of ions (K, bicarb and Na)
● Interlobular ducts:
- Large ducts located in the septa and line with stratified cuboidal-to-columnar epithelium.
Compare the amount of ions in saliva and blood plasma
Saliva has 7x potassium, 3x bicarbonate and 1/10 the sodium that the blood plasma has
Describe the mechanism of sIgA secretion
Trancytosis:
Exocytosis of sIgA at the apical surface
↑
Proteolysis of the receptor produces sIgA, the IgA in complex with the receptor fragment called secretory component
↑
Endocytosis occurs at base of the acinar cell
↑
IgA binds receptor on an acinar cell and IgA receptor mediates transcytosis of IgA into gland lumen
↑ Serous cells and intralobular duct cells produce IgA receptor ↑ Plasma cells secrete IgA dimer
Compare and contrast serous and mucous cells in salivary glands
Serous Acinar Cells: Secrete proteins (amylase, lysozyme, sIgA) Mucous Acinar Cells: Secrete mucus (heavily glycosilated protein)
Common features: Basal RER, Apical Junctional Complexes, Golgi, Myoepithelial Cells, Apical Secretory Vesicles and Small Lumen
Describe myoepithelial cells in salivary glands
● Reside within the
basal lamina
● Smooth muscle-like
● Triangular or
elongated nuclei
● Long contractile
processes
● Also present in
intralobular ducts
Describe striated interlobular ducts in salivary glands
● Up to 1.5 L of
saliva per day
● Saliva composition: 7x K+ 3x HCO3- 1/10 Na+ compared to blood plasma
● Basal striations: Cell membrane infoldings that house mitochondria
● Apical surface:
Tight junctions
The submandibular gland
Compound tubularacinar gland with both serous and mixed acini, but mostly serous.
Mixed acini: serous demilunes (fixation artifacts)
Serous cells secrete proteins including lysozyme, and some intralobular ducts are striated
The parotid gland
Compound acinar gland with ONLY serous acini. Secretes alpha-amylase and other proteins. Intercalated ducts are long, intralobular ducts are striated. Abundance of adipose tissue, look for adipocytes.
The sublingual gland
Compound tubuloacinar gland with mostly mucous acini. Some mixed acini with serous demilunes (fixation artifacts). Intralobular ducts are NOT striated.
Diagnostic features of the submandibular gland
Compound tubuloacinar gland ● Mostly serous acini; some mixed and mucous ● Mixed acini with serous demilunes ● Shorter intercalated ducts ● Mostly striated intralobular ducts
Describe the structure of the exocrine pancreas
Compound acinar gland, similar to parotid. It has lobules separated by connective tissue septa. Septa contain blood vessels, lymphatics, nerves and ducts.
What are the secretory products of the exocrine pancreas?
● Digestive proenzymes:
lipases
nucleases
amylases
proteases
● Pancreatic enzymes are inactive proenzymes that get activated by enterokinase cleavage in the duodenum.
● Bicarbonate:
alkaline, neutralizes stomach acid, creating optimum pH for pancreatic enzymes.
What is necrotizing pancreatitis?
Pancreatic enzyme-mediated inflammation due to gallstones, alcohol abuse, infections, drugs or trauma
Describe the special features of the exocrine pancreas
● Serous acini:
- Polarized serous cells.
- Abundant RER and Golgi.
- Zymogen granules - apical half of cell.
- Secretion is stimulated by cholecystokinin,
a hormone produced by enteroendocrine
cells in duodenum
● Lack of myoepithelial cells.
● Intercalated ducts:
- Protrude into acini as centroacinar cells.
- Produce bicarbonate.
- Lack secretory granules
- Secretin, produced by enteroedocrine
cells in the duodenum stimulates bicarb
● Intralobular ducts:
- Lack striations. - Also secrete bicarbonate-rich fluid.
● Interlobular ducts:
- Low columnar epithelium. - Also secrete bicarbonate-rich fluid.
Regulation in the exocrine pancreas
- Acidic chyme stimulates enteroendocrine cells in duodenum.
- Enteroendocrine cells release cholecystokinin and secretin.
- Cholecystokinin stimulates proenzyme secretion. Secretin stimulates HCO3- secretion.
Major diagnostic feature of the pancreas
Islets of Langerhans, found in the endocrine portion of the pancreas
Adenocarcinomas
Malignant tumors of glandular epithelium, some of the most common tumors in adults
Acne
chronic inflammation of obstructed sebaceous glands
What are the 4 principle layers of the digestive tract?
- Mucosa
- Submucosa
- Muscularis externa
- Serosa or adventitia
What is the function of the mesentery?
Binds the digestive tract to the abdominal wall
What are the 3 subdivisions of the mucosa?`
Lining epithelium, lamina propia and muscularis mucosae
What are the 3 main functions of the mucosa?
- protection
- absorption
- secretion
It has a lining mucosa and muscularis mucosa
At what points does the epithelium of the mucosa change?
The epithelium of the mucosa changes abruptly at junctions or sphincters between the major organs.
Describe the lamina proper of the mucosa
The lamina propia is a loose connective tissue resembling the storm of lymphoid organs that contains blood and lymphatic vessels as well as lymphatic tissue and wandering connective tissue cells such as plasma cells and eosinophils. It functions for support.
Describe the muscularis mucosae
The muscularis mucosae is a thin layer of smooth muscle that produces movement of the mucosa creating ridges and valleys that facilitate absorption and secretion. It functions in mucosal motility.
Describe the submucosa
A layer of connective tissue deep to and supporting the mucosa. It consists of dense irregular connective tissue containing blood vessels, lymphatic vessels and a nerve plexus - submucosal plexus, which controls muscle activity.
Where is submucosa found?
In the duodenum and esophagus. Note, it has glands.
Where is the submucosal plexus found, what’s its function and what is it called?
It’s called Meissner’s plexus, it is found at the submucosal periphery. Its nerve plexus controls muscle activity.
What is the muscularis externa?
The muscular wall of the GI tract, deep to the submucosa. It is composed of two relatively thick layers of smooth muscle: inner circular layer and outer longitudinal layer, between which the myenteric/Auerbach’s plexus is located.
